In specific regard to the application of the servocircuitry according to the invention to electrochemical cells, there has been development as evidenced by the above mentioned copending U.S. patent applications, of methods and circuitry for controlling the "ohmic drop". Positive feedback circuitry requiring current interruption and/or the addition of "catalytic" electric energy waves and the like, has been used with minimum satisfaction because of complications necessary in the circuitry and the introduction of annoying transients, together with limitations in bandwidths of the systems.
Two basic dynamic compensation techniques have been predominant in the past. They are, basically, two different methods to obtain an error signal from which the amount of positive feedback is controlled. In the first, a small externally generated ac potential intermixed with cell current data is processed to obtain a positive feedback control signal. In the second technique the cell current is periodically interrupted for a short period. The "double layer voltage" or "barrier layer" equivalent potential within the cell during the zero current interruption period is compared to the input potential to obtain the feedback control signal. The ac method requires not only an ac signal source, but also introduces an extraneous signal into the cell current, which in a real system is non-linearly related to the double layer voltage. An extraneous dc voltage is thereby generated. In addition, it requires signal processing which limits the response time severely. The second technique is bandwidth limited as well, and also requires extremely careful attention to switching transient suppression, switching synchronization and sample and hold synchronization in addition to signal processing.